1. Field of the Invention
The present invention relates to a process for the hydrogenation of aromatic hydrocarbons.
2. Description of the Prior Art
Hydrogenation processes in which aromatic compounds alone or contained in hydrocarbonaceous oils are hydrogenated in the presence of hydrogen and a suitable catalyst are known.
U.S. Pat. No. 3,655,551 discloses that Group VIII noble metals, such as palladium or platinum, on zeolites exhibit high hydrogenation activity such that if a substantially sulfur-free atmosphere is maintained, effective hydrogenation of aromatics can occur at 200.degree. to 500.degree. F., pressures of 500 to 3000 psig and a space velocity of 0.5 to 2.0 and those conditions may be correlated such that little or no cracking occurs (see col. 2, lines 29-34). A reversible poison such as ammonia may be added to the feed being hydrogenated to further repress the cracking activity of the catalyst (see col. 8, lines 58-65 and col. 1, lines 39-45).
U.S. Pat. No. 3,132,090 discloses a 2-stage cyclic hydrocracking process utilizing a catalyst that may comprise palladium-Y zeolite in the second stage. The hydrogen sulfide concentration in the second stage is adjusted to be alternatively high or low to operate the second stage at sour or sweet conditions. The sweet second stage is operated at a hydrogen sulfide concentration of less than 0.2, preferably less than 0.01 millimole hydrogen sulfide per mole hydrogen to maximize jet fuel and diesel fuel production.
U.S. Pat. No. 3,527,695 discloses a process for hydrogenation of aromatic hydrocarbons in feedstocks boiling within the range of 35.degree. to 125.degree. C. in the presence of a catalyst comprising palladium incorporated with a crystalline zeolite, preferably Y zeolite. For maximum hydrogenation activity, the sulfur content of the feed is desirably 0.1 to 10 wppm. The feed may be subjected to catalytic hydrodesulfurization prior to the hydrogenation.
U.S. Pat. No. 3,405,056 discloses use of a Y-type zeolite combined with a noble metal such as palladium (column 2, line 69 to column 3, line 4). The coked partially deactivated catalyst is used for hydrocracking under sweet conditions.
U.S. Pat. No. 3,779,899 discloses the use of platinum on a stablized Y zeolite (i.e. ultrastable Y zeolite) for hydrogenation of aromatic hydrocarbons, particularly monocyclic hydrocarbons without substantial hydrocracking.
U.S. Pat. No. 3,781,199 discloses a hydrocracking process utilizing an ammonia stable hydrocracking catalyst comprising a Group VIII metal hydrogenation component composited with a stabilized (i.e. ultrastable ) Y type crystalline aluminosilicate zeolite and an inorganic oxide component. A hydrocarbonaceous feed containing less than 10 wppm organic nitrogen in admixture with ammonia is hydrocracked with the ammonia resistant catalyst.
It has now been found that aromatic hydrocarbon streams comprising at least 15 wppm (weight parts per million) organic nitrogen contaminants can be hydrogenated with the noble metal-containing zeolitic catalyst if the partially deactivated catalyst is subjected to hydrogen stripping at least periodically.